|Publication number||US7345482 B2|
|Application number||US 11/334,811|
|Publication date||Mar 18, 2008|
|Filing date||Jan 17, 2006|
|Priority date||Jan 14, 2005|
|Also published as||US20060158190, WO2006076738A1|
|Publication number||11334811, 334811, US 7345482 B2, US 7345482B2, US-B2-7345482, US7345482 B2, US7345482B2|
|Inventors||Charles A. Saylor|
|Original Assignee||Invivo Corporation|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (14), Non-Patent Citations (7), Classifications (9), Legal Events (5)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present application claims the benefit of U.S. provisional patent application Ser. No. 60/643,963, filed Jan. 14, 2005, which is hereby incorporated by reference herein in its entirety, including any figures, tables, or drawings.
Presently, the three primary designs for high frequency volume coils are a shielded quad Helmholtz pair coil, a birdcage coil, and a TEM coil.
Embodiments of the invention pertain to a resonator for use in magnetic resonance imaging. Embodiments of the subject invention pertain to a high-field mode-stable resonator for use in magnetic resonance imaging. Embodiments also pertain to a method of generating and/or receiving rf magnetic fields in a field of view (FOV) for magnetic resonance imaging. Decoupling circuitry, not shown, can allow embodiments of the subject resonator to be utilized for generating and receiving rf magnetic fields in a field of view.
Although the embodiment shown in
In a specific embodiment, the conductors that are internal to the shield in the center part of the rf resonator go through a hole in the ring shield and are connected by capacitors to the outside of the shield. Making the capacitive connection outside of the shield advantageously keeps the high electric fields associated with the capacitor outside of the shield.
In a specific embodiment, the rf magnetic field, in the field of view (FOV), of the resonant mode, of the center structure, is similar to that shown in FIG. 11 of U.S. Pat. No. 5,557,247. The resonant structure within the shield of the subject resonator can be tuned so that the two orthogonal M=1 modes, also known as the imaging modes, are at the resonant frequency of the proton nucleus. The subject resonator can incorporate an extra resonant structure external to the shield. This extra resonant structure external to the shield can be strongly coupled to the resonant structure within the shield. The coupling can be accomplished, for example, across capacitors. In a specific embodiment, the external resonant structure is a transmission line resonator. In this way, the combination of the resonant structure within the shield and the transmission line resonator can behave as a single resonant structure.
The transmission line resonator can be constructed of microstrip sections and lumped elements. This transmission line resonator can be tuned to the M=1 mode while it is not coupled to the resonant structure within the shield. The transmission line resonator can provide a cyclic boundary condition transmission resonator that is one wavelength long at the resonant frequency. The design of the transmission line resonator can permit a large spacing in the frequency domain between the M=1 mode and both the M=0 and the M=2 modes. By coupling the resonant structure that is internal to the shield and the one external to the shield we obtain a new resonant structure that has a large spacing between modes in the frequency domain. In a specific embodiment, the spacing between M=1 mode and both the M=0 mode and the M=2 mode is a factor of 3, or more, greater than the bandwidth of the resonant. Preferably, the spacing is large enough such that the M=0 mode has less than 20% of the energy, more preferably less than 10% of the energy, and even more preferably, less than 5% of the energy. This large spacing permits us to substantially maintain the current distribution of the imaging mode even if the coil is heavily loaded, such as when an object to be imaged is inserted inside the resonator.
The coil in the embodiment of the subject invention shown in
In an embodiment, the shield is made in five sections along the z axis (z axis is defined by the static magnetic field direction in a horizontal field magnet). The shield lets gradient fields pass and shields rf fields. Referring to
Sections 2 and 4 in the embodiment shown in
Each of the elements in the resonator structure within the shield can include a capacitor connecting an inductive element, approx. 5 inches in length 0.125 diameter copper pipe, to the shield ring, and another capacitor connecting the other end of the inductive element to the other shield ring. Specific embodiments can break the inductive element into multiple segments that are connected by capacitors. The inductive elements can be made of other materials such as foil or solid metal rods. The use of tubes or rods allow a person to see out through the subject resonator when the resonator is over the person's head.
The transmission line can be constructed from a combination of microstrip and lumped elements to tune the transmission line to the resonant frequency. In an embodiment, the transmission line is a continuous line tuned to the first order mode, which is doubly degenerate, so that it is one full wavelength around the structure. In this case, doubly degenerate means the transmission line can support two current modes 90 degrees out of phase.
In the embodiment shown in
After tuning the resonant frequency of each of the individual elements of the resonator so that the M=1 mode of the coupled mode is on resonance and the resonant frequency of the transmission line, each element of the resonator can be overcoupled to the transmission line. Alternative orders and techniques for tuning can also be used. Because of the parallel resonant structure of the resonant element and the overcoupling of the elements to the transmission line, each of the elements in the structure appears as a high impedance to the transmission line. This results in very little change in the resonant frequency of the either the transmission line or the resonant mode of the elements. The resonant frequency can then be final tuned to adjust for any small shifts.
In a specific embodiment, an end plate that is an rf conducting plate can be placed in the transverse plane of the resonator. The rf conducting plate can have capacitor breaks in such a way to be rf conducting. An rf conducting plate can be located on the end of the resonator where the transmission line is located and/or an rf conducting plate can be located on the opposite end of the resonator from the transmission line.
All patents, patent applications, provisional applications, and publications referred to or cited herein are incorporated by reference in their entirety, including all figures and tables, to the extent they are not inconsistent with the explicit teachings of this specification.
It should be understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application.
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|1||Ballon, D. et al., A 64 MHz Half-Birdcage Resonator for Clinical Imaging, Journal of Magnetic Resonance, 1990, pp. 131-140, vol. 90, No. 1, Academic Press, Inc., Orlando, FL, US.|
|2||Bimson, W.E. et al., An Elliptical Cross Section Birdcage Body Coil, Book of Abstracts of the 11<SUP>th </SUP>Annual Scientific Meeting (Held Jointly with the Ninth Annual Congress of the European Society for Magnetic Resonance in Medicine and Biology), Meeting and Exhibition of the Society of Magnet, Aug. 8-14, 1992, p. 272, vol. 1, Meeting 11, Berlin, Germany.|
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|U.S. Classification||324/318, 324/322|
|Cooperative Classification||G01R33/422, G01R33/3456, G01R33/34046|
|European Classification||G01R33/422, G01R33/345A1, G01R33/34F|
|Feb 16, 2006||AS||Assignment|
Owner name: INVIVO CORPORATION, FLORIDA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:SAYLOR, CHARLES A;REEL/FRAME:017180/0865
Effective date: 20060213
|Sep 30, 2008||CC||Certificate of correction|
|Oct 31, 2011||REMI||Maintenance fee reminder mailed|
|Mar 18, 2012||LAPS||Lapse for failure to pay maintenance fees|
|May 8, 2012||FP||Expired due to failure to pay maintenance fee|
Effective date: 20120318